A sun-tanned appearance is a symbol of a healthy, dynamic, and active life. Yet, the damaging effects of sunlight and other sources of ultraviolet radiation on the skin are well documented. These effects are cumulative and potentially serious, and include sunburn, skin cancer, and premature aging of the skin. These effects associated with exposure to ultraviolet radiation are more fully discussed in DeSimone, "Sunscreen and Suntan Products", Handbook of Nonprescription Drugs, 7th Ed., Chapter 26, pp. 499-511 (American Pharmaceutical Association, Washington, D.C; 1982); Grove and Forbes, "A Method for Evaluating the Photoprotection Action of Sunscreen Agents Against UV-A Radiation", International Journal of Cosmetic Science, 4, pp. 15-24 (1982); and U.S. Pat. No. 4,387,089, DePolo, issued Jun. 7, 1983; the disclosures of all of which are incorporated herein by reference in their entirety.
Sunscreens are the most common agents used for sun protection. However, sunscreens also have the disadvantage of preventing or greatly diminishing the cosmetically desirable tanning response. Thus, if an individual uses a sunscreen for protection from ultraviolet radiation, he or she does so at the expense of foregoing a tanned appearance. Furthermore, even if an individual is willing to accept the risks associated with exposure to ultraviolet radiation to obtain a tan, there are situations in which it may not be practical or even possible to do so because of time constraints, weather conditions, etc. Therefore, it would be highly desirable to develop products for providing a tanned appearance to the skin, whenever desired without the need for exposure to ultraviolet radiation.
It is generally known that dihydroxyacetone, when applied topically to human skin, will produce a tanned appearance, i.e. an artificial tan. U.S. Pat. No. 4,708,865, to Turner, issued Nov. 24, 1987 describes the use of hydro-alcoholic solutions of dihydroxyacetone for tanning the skin; U.S. Pat. No. 4,466,805, to Welters, issued Aug. 21, 1984 describes hair and skin coloring formulations containing dihydroxyacetone; and U.S. Pat. No. 2,949,403, to Andreadis et al., issued Aug. 16, 1960 describes artificial tanning formulations containing dihydroxyacetone in an oleaginous base.
Dihydroxyacetone is relatively sensitive to heat, light, and moisture. It is known that products containing dihydroxyacetone generally have a short shelf life, tending to darken and develop disagreeable off-odors over time, with a concomitant loss of product performance. Dihydroxyacetone can react with other ingredients in a formulation, especially with nitrogen-containing compounds, such as amines, amino acids, and the like. In fact, without being limited by theory, dihydroxyacetone is believed to provide an artificial tan to human skin by its reaction with the nitrogen containing proteins of the skin. See L. Goldman et al., "Investigative Studies with the Skin Coloring Agents Dihydroxyacetone and Glyoxal", The Journal of Investigative Dermatology, vol. 35, pp. 161-164 (1960); E. Wittgenstein et al., "Reaction of Dihydroxyacetone (DHA) with Human Skin Callus and Amino Compounds", The Journal of Investigative Dermatology, vol. 36, pp. 283-286 (1961); and A. Meybeck, "A Spectroscopic Study of the Reaction Products of Dihdyroxyacetone With Amino Acids", J. Soc. Cosmet. Chem., 25-35 (1977); all of which are incorporated by reference herein in their entirety. This incompatibility of dihydroxyacetone with nitrogen containing compounds has limited the formulation scope of artificial tanning products in the past.
Conventional stablilizing agents and antioxidants such as BHA, BHT, and vitamin E are ineffective for stabilizing artificial tanning compositions containing dihydroxyacetone. Surprisingly, it is found in the present invention that certain salts such as metabisulfite salts, sulfite salts, and hydrogen sulfite salts greatly enhance the stability of artificial tanning compositions containing dihydroxyacetone. The use of metabisulfite salts as anti-oxidants is known in the pharmaceutical area, however, their use has typically been limited to extremely low levels, e.g. 0.005%. In the present invention, it is found that much higher levels of salts such as metabisulfite, sulfite, and hydrogen sulfite salts, i.e. levels in the range from about 0.025% to about 5%, provide an unexpected enhancement of stability. This enhanced stability translates into benefits such as increased product shelf life, good product performance, maintenance of the aesthetic characteristics of the product, i.e. less discoloration and off-odors, and better user acceptance.
It is therefore an object of the present invention to provide artificial tanning compositions useful for imparting an artificial tan to human skin.
It is another object of the present invention to provide artificial tanning compositions which exhibit improved chemical and physical stability.
It is another object of the present invention to provide artificial tanning compositions which have good color development characteristics such as providing a natural looking and rapidly developing tan.
It is another object of the present invention to provide artificial tanning compositions useful for both providing an artificial tan to human skin and for protecting human skin from the harmful effects of ultraviolet radiation.
It is another object of the present invention to provide a method for artificially tanning human skin.
It is another object of the present invention to provide a method for artificially tanning human skin and for providing protection from the harmful effects of ultraviolet radiation.
These and other objects of this invention will become apparent in light of the following disclosure.